Chloroplasts

Abstract

Chloroplasts are plastid, chlorophyll-containing organelles found in plant cells and eukaryotic algae that conduct photosynthesis. Chloroplasts and other plastids, such as etioplasts, leucoplasts, amyloplasts, and chromoplasts, develop either by division of an existing plastid or from proplastids. It is generally accepted that plastids are derived from a single endosymbiotic event in the ancestor of glaucophytes, red, and green algae (which was the ancestor of land plants). Understanding the origin of plastids enhances our understanding of the basis of photosynthesis in green plants, our primary food source.

The first three articles in this chapter review chloroplast division machinery in the unicellular red alga Cyanidioschyzon merolae and the glaucocystophyte Cyanophora paradoxa. Pyrenoids are sub-cellular compartments of chloroplasts in many algae, and their main function is to act as centers of carbon dioxide fixation in which RuBisCO is accumulated. Haematococcus pluvialis is a freshwater green algae which is well known for its accumulation of carotenoids (e.g., astaxanthin) during encystment. Cells of many lower land plants (i.e., archegoniate plants) contain only a single chloroplast. Riverweed, a unique aquatic angiosperm, has two different sizes of chloroplasts in each epidermal cell. The distribution of chloroplasts and mitochondria in mesophyll cells, prolamellar bodies of the etioplast in etiolated cotyledon, and chloroplast division machinery are highlighted and illustrated in several land plants. Finally, the active digestion of paternal chloroplast DNA in a young zygote of Chlamydomonas reinhardtii are presented.